Field of the Invention
The present disclosure relates to an electrophotography system image forming apparatus, such as a copier, printer, or the like.
Description of the Related Art
There has been known an electrophotography system image forming apparatus which has an intermediate transfer member. This image forming apparatus transfers a toner image formed on the surface of a photosensitive drum serving as an image bearing member, onto the intermediate transfer belt by applying voltage from a voltage power supply to a primary transfer member disposed at a position facing the photosensitive drum, as a primary transferring step. Subsequently, this primary transferring step is repeated for multiple toner image colors, thereby forming a toner image of multiple colors on the surface of the intermediate transfer medium. Thereafter, the multiple-color toner image formed on the surface of the intermediate transfer medium is transferred all at once onto a recording medium such as paper or the like, by applying voltage to a secondary transfer member, as a secondary transferring step. The toner image transferred all at once is then fixed fast onto the recording medium by a fixing unit, thereby forming a color image.
Japanese Patent Laid-Open No. 2012-137733 discloses a configuration in which voltage is applied to a current supply member which contacts an intermediate transfer belt serving as an intermediate transfer medium. This aims to reduce costs and size of the image forming apparatus by doing away with a high-voltage power source dedicated to primary transfer. According to this configuration, current is supplied to multiple photosensitive drums in the peripheral direction of the intermediate transfer belt to perform primary transfer of the toner image onto the intermediate transfer belt. Also disclosed is a configuration where the intermediate transfer belt is connected to a stretching roller over which the intermediate transfer belt stretched via a voltage maintaining element (e.g., a Zener diode), to prevent attenuation of primary transfer voltage at each image forming station.
Also, there is known a configuration where correction control to correct relative position shifting of the toner images of each color, and correction control to correct change in toner density of each color, are periodically performed by detecting members detecting a test pattern formed on the surface of the intermediate transfer member. In Japanese Patent Laid-Open No. 2012-230250, a detecting member is disposed at an opposing position to the stretching roller.
However, disposing a detecting member at an opposing position to a stretching roller as described in Japanese Patent Laid-Open No. 2012-230250, in the configuration described in Japanese Patent Laid-Open No. 2012-137733, the following problem arises. That is to say, a Zener diode is connected at the stretching roller where the detecting member faces, so a predetermined potential is generated at a region on the intermediate transfer belt facing the detecting member. This potential may cause discharge between the stretching roller and detecting member, or floating toner to adhere to the intermediate transfer belt. These may cause deteriorated test pattern detection accuracy.